[CP-6265] Sign all files in installer build

Allowing us to make code signing optional

We do not sign cat files when all drivers are marked as being WHQL signed
as this prevents us overwriting the MS signature.

Signed-off-by: Ben Chalmers <Ben.Chalmers@citrix.com>
Merge pull request #18 from benchalmers/cp-6265-2

[CP-6265] Sign all files in installer build